How rapidly would the signal fade if a cell phone (at 800 MHz) is in a car moving at 100 km/h?

How rapidly would the signal fade if a cell phone (at 800 MHz) is in a car moving at 100 km/h?

How rapidly would the signal fade if a cell phone (at 800 MHz) is in a car moving at 100 km/h?
How rapidly would the signal fade if a cell phone (at 800 MHz) is in a car moving at 100 km/h?